Single crystals of high-purity copper, having two different orientations, were pressed through one pass in equal-channel angular pressing (ECAP) at room temperature and then examined using several different analytical techniques. For both orientations, it is shown that elongated arrays of cells or subgrains are formed in the first pass with their long axes aligned parallel to the primary ((1) over bar(1) over bar(1) over bar)[(1) over bar 10] slip system. The average width of these subgrains was measured as similar to 0.2 mu m which is similar to the equilibrium grain size reported in polycrystalline Cu after processing by ECAP. These results confirm earlier observations using an aluminum single crystal except only that the subgrain width in copper is significantly smaller. This difference is attributed to the lower stacking-fault energy in copper and the consequent low rate of recovery.